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CO2-dependent opening of an inwardly rectifying K+ channel.

Huckstepp RT, Dale N - Pflugers Arch. (2011)

Bottom Line: This reversal potential was shifted by +61 mV following a tenfold increase in extracellular [K(+)] but was insensitive to variations of extracellular [Cl(-)].We propose that this channel is a member of the Kir family.In addition to this K(+) channel, we found that many of the excised patches also contained a conductance carried via a Cl(-)-selective channel.

View Article: PubMed Central - PubMed

Affiliation: School of Life Sciences, University of Warwick, Coventry, CV4 7AL, UK.

ABSTRACT
CO(2) chemosensing is a vital function for the maintenance of life that helps to control acid-base balance. Most studies have reported that CO(2) is measured via its proxy, pH. Here we report an inwardly rectifying channel, in outside-out excised patches from HeLa cells that was sensitive to modest changes in PCO(2) under conditions of constant extracellular pH. As PCO(2) increased, the open probability of the channel increased. The single-channel currents had a conductance of 6.7 pS and a reversal potential of -70 mV, which lay between the K(+) and Cl(-) equilibrium potentials. This reversal potential was shifted by +61 mV following a tenfold increase in extracellular [K(+)] but was insensitive to variations of extracellular [Cl(-)]. The single-channel conductance increased with extracellular [K(+)]. We propose that this channel is a member of the Kir family. In addition to this K(+) channel, we found that many of the excised patches also contained a conductance carried via a Cl(-)-selective channel. This CO(2)-sensitive Kir channel may hyperpolarize excitable cells and provides a potential mechanism for CO(2)-dependent inhibition during hypercapnia.

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Current–voltage characteristics and permeability of the CO2-sensitive channel. a Single-channel gating in outside-out excised patches during a series of 10 mV steps from +20 mV to –70 mV (left to right) in control 3 and 30 mM K+ aCSF at a PCO2 of 70 mmHg. b Current–voltage plots of the single-channel currents in 3 mM K+ (n = 4) and 30 mM K+ (n = 4) aCSF. The reversal potential changed from –70 mV to –9 mV and the slope conductance of the channel was increased by elevating extracellular K+. c Plot of the open probability (Po) against membrane potential for three excised patches, measured in 30 mM K+ aCSF. Po exhibited no voltage dependence. Bars are SEMs
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Fig3: Current–voltage characteristics and permeability of the CO2-sensitive channel. a Single-channel gating in outside-out excised patches during a series of 10 mV steps from +20 mV to –70 mV (left to right) in control 3 and 30 mM K+ aCSF at a PCO2 of 70 mmHg. b Current–voltage plots of the single-channel currents in 3 mM K+ (n = 4) and 30 mM K+ (n = 4) aCSF. The reversal potential changed from –70 mV to –9 mV and the slope conductance of the channel was increased by elevating extracellular K+. c Plot of the open probability (Po) against membrane potential for three excised patches, measured in 30 mM K+ aCSF. Po exhibited no voltage dependence. Bars are SEMs

Mentions: We examined how the single-channel currents altered with voltage (Fig. 3a). The single-channel current exhibited inward rectification (Fig. 3b). The conductance of the channel was 6.7 ± 0.5 pS (calculated from the linear portion of the I–V relation, n = 4, Fig. 3b) and the single-channel currents reversed at –70 mV (Fig. 3a, b). This reversal potential lay between the K+ and Cl– equilibrium potentials calculated to be –93 mV and –20 mV, respectively. Interestingly Po showed little variation at different potentials (Fig. 3c).Fig. 3


CO2-dependent opening of an inwardly rectifying K+ channel.

Huckstepp RT, Dale N - Pflugers Arch. (2011)

Current–voltage characteristics and permeability of the CO2-sensitive channel. a Single-channel gating in outside-out excised patches during a series of 10 mV steps from +20 mV to –70 mV (left to right) in control 3 and 30 mM K+ aCSF at a PCO2 of 70 mmHg. b Current–voltage plots of the single-channel currents in 3 mM K+ (n = 4) and 30 mM K+ (n = 4) aCSF. The reversal potential changed from –70 mV to –9 mV and the slope conductance of the channel was increased by elevating extracellular K+. c Plot of the open probability (Po) against membrane potential for three excised patches, measured in 30 mM K+ aCSF. Po exhibited no voltage dependence. Bars are SEMs
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC3037493&req=5

Fig3: Current–voltage characteristics and permeability of the CO2-sensitive channel. a Single-channel gating in outside-out excised patches during a series of 10 mV steps from +20 mV to –70 mV (left to right) in control 3 and 30 mM K+ aCSF at a PCO2 of 70 mmHg. b Current–voltage plots of the single-channel currents in 3 mM K+ (n = 4) and 30 mM K+ (n = 4) aCSF. The reversal potential changed from –70 mV to –9 mV and the slope conductance of the channel was increased by elevating extracellular K+. c Plot of the open probability (Po) against membrane potential for three excised patches, measured in 30 mM K+ aCSF. Po exhibited no voltage dependence. Bars are SEMs
Mentions: We examined how the single-channel currents altered with voltage (Fig. 3a). The single-channel current exhibited inward rectification (Fig. 3b). The conductance of the channel was 6.7 ± 0.5 pS (calculated from the linear portion of the I–V relation, n = 4, Fig. 3b) and the single-channel currents reversed at –70 mV (Fig. 3a, b). This reversal potential lay between the K+ and Cl– equilibrium potentials calculated to be –93 mV and –20 mV, respectively. Interestingly Po showed little variation at different potentials (Fig. 3c).Fig. 3

Bottom Line: This reversal potential was shifted by +61 mV following a tenfold increase in extracellular [K(+)] but was insensitive to variations of extracellular [Cl(-)].We propose that this channel is a member of the Kir family.In addition to this K(+) channel, we found that many of the excised patches also contained a conductance carried via a Cl(-)-selective channel.

View Article: PubMed Central - PubMed

Affiliation: School of Life Sciences, University of Warwick, Coventry, CV4 7AL, UK.

ABSTRACT
CO(2) chemosensing is a vital function for the maintenance of life that helps to control acid-base balance. Most studies have reported that CO(2) is measured via its proxy, pH. Here we report an inwardly rectifying channel, in outside-out excised patches from HeLa cells that was sensitive to modest changes in PCO(2) under conditions of constant extracellular pH. As PCO(2) increased, the open probability of the channel increased. The single-channel currents had a conductance of 6.7 pS and a reversal potential of -70 mV, which lay between the K(+) and Cl(-) equilibrium potentials. This reversal potential was shifted by +61 mV following a tenfold increase in extracellular [K(+)] but was insensitive to variations of extracellular [Cl(-)]. The single-channel conductance increased with extracellular [K(+)]. We propose that this channel is a member of the Kir family. In addition to this K(+) channel, we found that many of the excised patches also contained a conductance carried via a Cl(-)-selective channel. This CO(2)-sensitive Kir channel may hyperpolarize excitable cells and provides a potential mechanism for CO(2)-dependent inhibition during hypercapnia.

Show MeSH
Related in: MedlinePlus